The present invention relates to a valve of type including a valve body having a stationary valve seat and a valve member having a movable valve seat co-operative with said stationary seat. The present invention further relates to a method for manufacturing a valve of the type referred to above.
Various types of valves have been known and widely used for various applications. These valves include such a type which has a valve body and a movable valve member having co-operative seat surfaces. In order to reduce wear of the seat surfaces, this type of valve usually includes seat members of hard material which are respectively provided on the valve body and the valve member by thread engagement or welding technique. However, the known seat constructions are disadvantageous in various respects. When the seat is attached to the valve body or valve member through thread means, fluid seepage may occur at the thread portion due to distortion or loosening of thread engagement. Further, the provision of the thread portion will require an increased thickness, so that an increased amount of relatively expensive seat material must be used and that the weight of the seat is increased. The increased thickness of the seat on the valve member causes an increase in thickness of the valve member itself resulting in an increase in the movable mass of the valve member. Thus, in this type of valve, a substantial force is required to move the valve member. Further, the increase in dimension of the valve member causes an increase in dimension of the valve body and thus an increase in the total weight of the valve. Still further, this type of valve requires a substantial labour in forging, thread forming, tempering and assembling the same.
In a valve in which seat members are welded on a valve body and valve member, it is impossible to employ corrosion resistant materials such as titanium and zirconium because they do not accept welding. When materials other than those of corrosion resistant type are used, corrosion of the valve material will reduce the life of the valve. Further, this type of valve is also disadvantageous in that increased labour is required in removing welding beads, tempering and machining the valve parts. These problems may be overcome by forming the seat integrally with the valve body or the valve member using a seat material, however, this type of solution is not practical in a usual valve since it requires a large amount of relatively expensive material.